PROJECT SUMMARY The ability of the brain to utilize information from past experiences to guide future decisions, termed adaptive behavior, is critical for survival. To effectively adapt behaviors, the brain applies stored memory to new but similar situations (generalization), while also maintaining the capacity to distinguish unique stimuli (discrimination). When these critical processes (memory generalization or discrimination) go awry, it can lead to maladaptive disorders such as post-traumatic stress disorder (PTSD) and panic disorder. Despite their importance, mechanisms underlying memory discrimination and generalization remain largely unknown. This proposal will investigate the dynamic processes that underlie the utilization of an encoded memory to guide future behaviors, in particular the molecular, synaptic, and circuit mechanisms that govern the balance between discrimination and generalization. We have collected very exciting preliminary data showing that individual contextual fear memories are represented in the dentate gyrus (DG) by multiple functionally distinct neuronal ensembles defined by different activity-dependent transcriptional pathways, and that these ensembles bi-directionally regulate the discrimination-generalization balance. Based on these exciting findings, we hypothesize that the activity- dependent pathways target specific synaptic inputs on DG granule cells to differentially control memory discrimination and generalization. We aim to (1) uncover novel forms of learning-induced synaptic plasticity; (2) reveal underlying circuit mechanisms for memory discrimination and generalization; and (3) identify the molecular players important for this experience-dependent behavioral adaptation. The proposed research is both conceptually and technically innovative. It will experimentally demonstrate for the first time functionally distinct active neuronal ensembles coexisting within the memory engram, shed light on the synaptic and circuit mechanisms by which encoded memories directly drive experience-dependent behavioral outputs, and may lead to new treatment strategies for neuropsychiatric disorders, such as PTSD and panic disorder, which are caused by the imbalance between memory discrimination and generalization.